This invention relates to coextrusion of sheet and film product, particularly to edge-lamination, especially of thermoplastic compositions such as synthetic resins.
Forming a composite stream, in particular an edge-laminated composite stream, in a feedblock is described in U.S. Pat. No. 4,784,815 to Cloeren and Werney. Forming a composite stream in a die manifold is illustrated by U.S. Pat. No. 3,715,420 to Kiyono. Forming an edge-laminated composite stream downstream of a die manifold is exemplified by German patent document 2,851,930. In each of the foregoing patent documents, flow pressure of one stream is utilized to displace a portion of another stream.
Mechanically dividing a single manifold into segments and forming an edge-laminated sheet downstream of the manifold is illustrated by U.S. Pat. No. 4,533,510 to Nissel. The use of an apparatus in which the manifolds or flow channels are vertically oriented relative to one another, to form a composite stream, is exemplified by U.S. Pat. Nos. 4,197,069 to Cloeren and U.S. Pat. No. 4,410,602 to Komoda et al.
The formation of a composite sheet in an extrusion die including side-by-side die manifolds, is illustrated by U.S. Pat. No. 4,476,075 to Brinkmann et al, U.S. Pat. No. 4,562,023 to Pabst et al, and U.S. Pat. No. 4,521,359 to Tsein. Brinkmann et al and Pabst et al describe sheet formed from a colorless stream and a dyed stream of polyvinyl butyral. Tsein describes sheet formed from elliptically shaped streams matched with respect to their melt indices.
Extruded product including a core that may be one or more layers, and including a narrow or wide edge layer on one or both sides of the core, is commercially available. However, a difficulty exists in providing a sharp and well-defined edge seam or boundary when the seam is formed by converging streams of dissimilar rheological properties.
Accordingly, there remains a need for an improved extrusion apparatus and process that are advantageous for converging streams, and in particular a core stream and an edge-laminating stream, of dissimilar rheological properties. Beneficially, such an apparatus would provide an edge seam that is sharp and well-defined. Advantageously, such an extrusion apparatus could mechanically define the width of an edge of an edge-laminated product.